[CentOS] Analyzing the MBR

Thu Jun 5 19:07:21 UTC 2014
Timothy Murphy <gayleard at eircom.net>

John R Pierce wrote:

> On 6/5/2014 10:47 AM, Timothy Murphy wrote:
>> Is this strictly true - that only the MBR is read at boot-time?
> the MBR has two elements.
> A) the boot code, which is read and executed by the BIOS at boot time,
> only on the boot drive
> and
> B) the master partition table, which is read on any drive when its
> inserted

That doesn't really answer my question;
I know (roughly) what the MBR, ie the first 512 bytes, contains.
But I notice that my laptop, for example, leaves 64 sectors
for something at the start of the disk;
and when I get the first 2048 bytes with
  sudo dd if=/dev/sda of=sda.mbr bs=2048 count=1
I see that there is plenty on the disk after the first 512 bytes.
(Admittedly Windows might have written that, as I have a Windows partition.)
But does Linux ever write anything in bytest 513-1024, for example?

Does grub2 write more than CentOS grub?
It seems to me to be difficult to have CentOS and Fedora 
as alternative OSs on the same machine?

Timothy Murphy  
e-mail: gayleard /at/ eircom.net
School of Mathematics, Trinity College, Dublin 2, Ireland